Sen. John McCain, R-Ariz. talks to reporters on Capitol Hill in Washington, on March 5, after making an appeal on the floor of the Senate for the US to lead an 'international effort' involving air strikes on Syria's military forces.

"The President must state unequivocally that under no circumstances will Assad be allowed to finish what he has started, that there is no future in which Assad and his lieutenants will remain in control of Syria, and that the United States is prepared to use the full weight of our airpower to make it so."

There is certainly reason for alarm from a humanitarian and moral point of view. As McCain said: "The kinds of mass atrocities that NATO intervened in Libya to prevent in Benghazi are now a reality in Homs," Senator McCain said. "Indeed, Syria today is the scene of some of the worst state-sponsored violence since Milosevic’s war crimes in the Balkans, or Russia’s annihilation of the Chechen city of Grozny."

That's pretty much right. Weeks of shelling of Homs, particularly the Baba Amr neighborhood of that city that was a stronghold for anti-Assad insurgents and the activists working with them, have killed scores. Satellite images purchased and analyzed by Human Rights Watch show mortar and rocket strikes on well over 100 buildings in the densely packed neighborhood. And reports from activists have claimed that since the opposition Free Syrian Army was routed from the city last week, opposition supporters have been massacred in the streets and tortured in detention centers.

I was in Benghazi the morning last year that French planes, later joined by British, US, and other NATO airpower, stopped Muammar Qaddafi's march on the city cold and began the process of turning the tide in favor of his opponents. Everything I've read and seen coming out of Homs in recent weeks jibes with what I expected would have been Benghazi's fate if NATO had not come to the Libyan rebellion's aid.

But unfortunately for Syria's opposition, the international cavalry is not coming any time soon. Nearly a year into the war to oust Assad, the Syrian army remains largely intact. In the case of Libya, there were mass defections from Qaddafi's forces within days of protests breaking out against his rule. And the Libyan army of Qaddafi was far less capable than Syria's army under Assad. Its forces were not as well-trained, as well-led, or as well-armed.

If air power were to be used against Assad's regime as it was used to overthrow Qaddafi's, then the venture will take longer than the six months it took in Libya. The price in Syrian blood, on both sides will be higher, and the geography of the country -- without the vast stretches of desert between towns that were turned into shooting galleries when Qaddafi tried to move his forces -- would guarantee more civilian casualties from NATO bombs than occurred in Libya.

And though some are suggesting that civilian protections zones be carved out, and suggest that as a panacea, fighting will have to be done to accomplish that (Peter Munson, a skeptic on intervention in Syria, looks at some of the risks). Finally, Russia and China have vowed to stand in the way of UN Security Council authorization to act, instead of standing aside, as they did in the case of Libya.

McCain continued today: "The problem is, the bloodletting continues. Despite a year’s worth of diplomacy backed by sanctions, Assad and his top lieutenants show no signs of giving up and taking the path into foreign exile. To the contrary, they appear to be accelerating their fight to the finish. And they are doing so with the shameless support of foreign governments, especially in Russia, China, and Iran."

The senator is again right. Assad, like Qaddafi before him, does not want to yield power, nor do the many hundreds of thousands of Syrians who have benefited from his regime, particularly his fellow Alawites. This is a real rock and a hard place situation: Assad is nowhere near ready to quit (and for a reminder on how long sanctions can be withstood, Saddam Hussein handled more than a decade of economic isolation after the Gulf War). But the costs of international action could be high. And it's not clear what allies the US would go to war with if it takes McCain's advice.

"The United States should lead an international effort to protect key population centers in Syria, especially in the north, through airstrikes on Assad’s forces. To be clear: This will require the United States to suppress enemy air defenses in at least part of the country," McCain said today.

He outlines an effort much like the one in Libya. But again, Syria is larger (20 million citizens against 6 million in Libya), Assad's defenders are strong.

“The ultimate goal of airstrikes should be to establish and defend safe havens in Syria, especially in the north, in which opposition forces can organize and plan their political and military activities against Assad. These safe havens could serve as platforms for the delivery of humanitarian and military assistance – including weapons and ammunition, body armor and other personal protective equipment, tactical intelligence, secure communications equipment, food and water, and medical supplies. These safe havens could also help the Free Syrian Army and other armed groups in Syria to train and organize themselves into more cohesive and effective military forces, likely with the assistance of foreign partners. “The benefit for the United States in helping to lead this effort directly is that it would allow us to better empower those Syrian groups that share our interests – those groups that reject Al-Qaeda and the Iranian regime, and commit to the goal of an inclusive democratic transition, as called for by the Syrian National Council. If we stand on the sidelines, others will try to pick winners, and this will not always be to our liking or in our interest. This does that mean the United States should go it alone. We should not. We should seek the active involvement of key Arab partners such as Saudi Arabia, U.A.E., Jordan, and Qatar – and willing allies in the E.U. and NATO, the most important of which in this case is Turkey.

McCain's full prepared statement is worth a read. While he's unlikely to get what he wants anytime soon, the horrors in Syria appear to be increasing, and the calls for international action are likely to get louder. At some point in the future, views like McCain's may end up carrying the day.